Big brother is helping you … success of eldest child can have ‘spillover’ effect, boosting exam results of their younger brothers and sisters

It is the first study to look at the impact of siblings, rather than influence of parents, on exam results and the researchers took elaborate steps to factor out other considerations.

Rabe said: “How much a younger child’s school achievement is affected by their brother’s or sister’s achievement is a really important question to answer, as it helps us understand whether investments in children may have multiplier effects.

“We found that the sibling spillover effect is larger in families eligible for free school meals, living in deprived neighbourhoods and speaking a language other than English at home. This means that children from more deprived backgrounds benefit more from a high-attaining older sibling than children from more affluent backgrounds. It may be that the effect arises through information-sharing about educational choices and schools or teachers. Information on this is likely to be harder to come by in poorer families, and the benefit to younger children is therefore high.”

She said that the conclusion for policymakers had to be that it was even more worthwhile to invest in enhancing the progress of children from deprived families when it was clear that the impact of that investment would be multiplied for their younger siblings.